Ethology of Laphria Fernaldi (Back) (Diptera: Asilidae) in Southeast Wyoming1
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25 April 1984 PROC. ENTOMOL. SOC. WASH. 86(2), 1984, pp. 326-336 ETHOLOGY OF LAPHRIA FERNALDI (BACK) (DIPTERA: ASILIDAE) IN SOUTHEAST WYOMING1 R. J. LAVIGNE AND S. W. BULLINGTON Entomology Section, University of Wyoming, Box 3354, University Station, Laramie, Wyoming 82071. -------------------------------- Abstract.—-The behavior of a western coniferous forest asilid, Laphria fernaldi (Back), was studied in southeast Wyoming. Prey, predominantly Coleoptera and Hymenoptera, are captured in aerial flights. No prey manipulation occurs once the asilid returns to the feeding site. Mating without prior courtship is completed on perch sites one to nine meters above the forest floor. -------------------------------- Described by Back (1904) as Dasyllis fernaldi, this species was subsequently placed in the genus Bombomima by Enderlein (1914). There it remained until Nagatomi (1964) synonomized Bombomima with Laphria, thus placing fernaldi in the latter genus. This change of status was supported by Martin (1965). This species, like other species formerly placed in Bombomima and species in the genus Mallophora, strongly resemble bumblebees in size, shape and color patterns and have been referred to as mimics (Bromley, 1930). Toads, at least, quickly learn to associate these color patterns with stinging hymenopteran models after one error of judgment (Brower et al., 1960) suggesting that this is batesian mimicry. Waldbauer and Sheldon (1971) maintain that for Laphria flavicollis Say and L. thoracica Fabricius, insectivorous birds are the main selective agents which determine the morphology and behavior of the mimics. A widespread distribution has been attributed to L. fernaldi in the western United States and Canada, specimens being cited from: Colorado (type locality) (Back, 1904;Cockerell, 1917;James, 1938, 1941); Nebraska, South Dakota (Jones, 1907); Oregon (Cole and Lovett, 1921); Utah (Brown, 1929; Knowiton and Harn- ston, 1938); Washington, Idaho, New Mexico, Arizona, Montana (Adisoemarto, 1967); British Columbia (Criddle, 1921) and Alberta (Adisoemarto, 1967). Be- cause there appears to be a complex of species involved (Bullington, unpublished data), some of these records may be in error. However, comparison of specimens from our study population with specimens taken from a variety of locations in Colorado have convinced us that the specimens referred to in the present paper are definitely Laphria fernaldi. METHODS James (1938) refers to B. fernaldi as a coniferous forest denizen and it is within a predominantly lodgepole pine forest that our study was conducted. The study --------------- ' Published with the approval of the Director, Wyoming Agricultural Experiment Station, as Journal Article No. JA 1224. VOLUME 86, NUMBER 2 327 site was located in the Snowy Range Mts., Albany Co., Wyoming, in a moderately wooded area across the North Fork of the Little Laramie River from the USFS North Fork Campground (elev. 2577 m). The area was bisected by an old logging road which at one point expanded into a large clearing. Most recorded activities were within the forest bordering the clearing. Fallen and cut logs of various dimensions were scattered over the forest floor, but most branches and small dead trees had been removed by campers seeking firewood. Methods of study of this population were similar to those described in Lavigne (1982) for Neoitamus vittipes. Additionally, individuals were marked by placing dots of various colors of Testers model airplane paint (Pla Enamel, the Testor Corporation, Rockford, Illinois) on the dorsum of the thorax. Each specimen was marked the first time it was encountered and had a specific designation, such as B3 (= 3 blue dots). With this method we individually marked 12 specimens in 1978 (12 G), 3 in 1979 (2 G, 1 E) and 43 in 1981 (36 G, 7 E). A few additional observations were made on a small population at Battle Creek Campground, Sierra Madre Mts., July 25-26, 1978. Extensive observations were made on this species in 1978 (7/25-9/9) and again in 1981 (7/16-9/20), while we were engaged in a study of male territoriality (Lavigne and Bullington, unpublished data). Incidental observations also were made during the adult flying season in 1979 (7/21-9/9) when time permitted. Specimens upon which this paper is based have been placed in the entomological collection of the Smithsonian Institution, Washington, DC as: R. J. Lavigne, Voucher Spec. #47. Weather conditions appeared to be the dominating influence on L. fernaldi activities during all three years. Activities largely ceased on cloudy days and on rainy days the asilids would disappear. Intermittent rain showers or all day rains were common in August, thus limiting opportunities for the flies to feed, mate and oviposit. Each sunny morning male L. fernaldi would appear on rocks or on logs between 0845 and 1005 h, whenever the log surface temperature reached ca. 27°C. In late afternoon between 1700 and 1800 h, the asilids usually would leave the logs. Followed males flew 20-25 m in interrupted flights eventually disappearing into the tree canopy, where it is presumed they spent the night. As the season progressed and the angle of the sun changed, logs would be sunlit for shorter periods and asilids would leave them at an earlier time. FORAGING AND FEEDING BEHAVIOR All observed Laphria fernaldi males foraged from sunny spots on logs (Fig. 1) which they constantly patrolled. We speculate that females foraged within the tree canopy. In only five instances over a four year period were females observed with prey in the study area; in four, the female was resting in sunlight on the surface of a log. The remaining female was found clinging to a rock in a clearing with a bumblebee as prey. The sky was cloudy. Other observed females were engaged in mating, oviposition, or resting but never foraging. Subsequent foraging data refer to male activity. The heads of males are almost constantly in motion presumably in order to evaluate both potential prey and potential mates and/or competitors. Often the whole body is turned. Attack flights are initiated from log surfaces in response to moving insects. However, apparently particular characteristics of potential prey 328 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON are important in stimulating an attack since a great variety of insects are ignored, though obviously seen. Once initiated, the prey capture dart may be a straight line attack or, if the potential prey, such as a syrphid or dragonfly exhibits evasive action (N = 6), the chase may be a long and convoluted flight. Observed foraging flights ranged from 1/3 m to 11 m. Unsuccessful flights (N = 51) covered the same distances, whereas successful capture darts (N = 11) covered l/3 to 7 m. It is interesting, however, that the means for successful capture darts (x = 11.8 m) are very close to those for unsuccessful ones (x = 12.3 m). All prey were collected while airborne (N = 20). Contact and capture may not mean that the prey is impaled. Six additional capture darts ended with the release of the collected item before the asilid landed. Prey selection apparently functions on the basis of visual discrimination. On four occasions, asilids circled insects (all bees) and then returned to their perch without making an attack suggesting a learned response. Another time a male flew halfway towards a small bee and then returned to its log. Conversely, errors are made. In one case a dandilion seed was the captured item, not an insect. Once prey are captured they are manipulated and impaled during a short hover prior to landing. The prey was usually still struggling when the asilid landed with the prey positioned (Fig. 2), facing forward, between its legs. Unlike most other asilid species, no manipulation takes place during feeding. The length of time males spend feeding is inordinately short in comparison to that spent by other asilids whose prey are proportionately large. For example, the mean feeding time for three specimens of the cantharid, Podabrus lateralis LeConte, was 4 min. Complete feeding times were recorded for 13 prey, ranging from 2 to 27 min (x = 9.5). Feeding asilids were often forced to move quickly with prey impaled upon their probosces. In one instance, an ant grabbed a feeding asilid's leg who responded by flicking off the ant and flying to a new perch. In addition to foraging ants, asilids responded to moving spiders. Larger predators were also a potential dis- turbance. Various species of birds hawked in the vicinity of the logs and both chipmunks and squirrels used the logs as runways. While feeding was in progress, and even afterwards, small numbers of tiny flies flitted about the asilid's proboscis. Some landed on the proboscis and others on the prey where the partially digested contents oozed from the open wound. When the harrassment was too great, the asilid would fly rapidly to a new perch. Once feeding ceased prey were discarded in one of two ways: in flight (N = 16) or when the asilid pushed the prey off its proboscis with its foretarsi on site (N = 10). The logs from which the asilids foraged, were partially decayed and often housed colonies of carpenter ants, Camponotus sp. Those that didn't, usually served as roofs for nests of Formica sp. Both kinds of ants were constantly foraging and discarded prey were quickly collected and taken into the nests. While male foraging activity has been observed as early as 0845 h (log surface temp. 23°C) and as late as 1729 h (log surface temp. 31°C), feeding records only cover the hours 0928 to 1649. The five female feeding records cover the time period 1120 h to 1537 h. PREY SELECTION Records of prey taken by bumblebee mimetic Laphria are few. Bromley (1930) states that this group of asilids "seem to prefer as prey, insects of the 'buzzing' VOLUME 86, NUMBER 2 329 Fig.